The present invention relates generally to an exposure apparatus, and more particularly to an exposure apparatus used to fabricate various devices including semiconductor chips such as ICs and LSIs, display devices such as liquid crystal panels, sensing devices such as magnetic heads, and image pick-up devices such as CCDs, as well as fine patterns used for micromechanics. The present invention is suitable, for example, for a scanning exposure apparatus that has an arc-shaped exposure area.
A reduction projection exposure apparatus has been conventionally employed which uses a projection optical system to project a circuit pattern formed on a mask or a reticle, which are referred to as an original in this application, onto a wafer, etc. to transfer the circuit pattern, in manufacturing such a fine semiconductor device as a semiconductor memory and a logic circuit in photolithography technology.
The projection exposure apparatuses have been required to enlarge the transfer area and improve the resolution so as to manufacture highly integrated semiconductor devices. Accordingly, the current main stream replaces a step and scan manner that exposes a reduced exposure image on a reticle at one time by sequentially moving each exposure area on the wafer to an exposure area of the projection optical system with a slit scan manner or a step and scan manner that enlarges the transfer area by synchronously scanning the reticle and the wafer.
Since the slit-scan projection exposure apparatus scan-exposes each exposure area on the wafer by using a rectangular opening that is shorter than a length in the scan direction of the exposure area, the accumulated exposure dose of the rectangular opening should be made constant for all the points on the wafer and the accumulated exposure dose should be controlled for each exposure area. When the accumulated exposure dose differs for each point on the wafer, the uneven accumulated exposure dose for each exposure area (or the uneven exposure) deteriorates the resolution.
Accordingly, various exposure apparatuses have been proposed to correct the uneven exposure by arranging, in place optically conjugate with the reticle, an exposure area shaping means for regulating an opening width according to the exposure non-uniformity. See, for example, Japanese Patent Applications, Publications No. 2001-244183 and 10-340854. For example, an exposure area shaping means 100 is configured to correct the uneven exposure dose irradiated on the wafer by a flexible blade 1100 that is obliquely attached to the optical axis of the exposure light, as shown in FIG. 7. A pair of blades 1100 are provided opposite to each other with respect to the optical axis, although FIG. 7 shows only one of the blades 1100. The blade 1100b is deformed to an arbitrary shape and a shape of the exposure area 1300 is determined by pushing and pulling tops 1200a and 1200e provided at outer correcting positions, tops 1200b and 1200d provided at inner correcting positions, and a top 1200c provided at center correcting position. The tops 1200a and 1200e are provided around the exposure area 1300 so as to maintain the uneven exposure around the exposure area 1300 when only the tops 1200b and 1200c are pushed and pulled so as to correct the uneven exposure near the inner correcting position. Here, FIG. 7 is a view for explaining a structure of the conventional exposure area shaping means 1000.
Another exposure area shaping means 200 is proposed as shown in FIG. 8, to correct the uneven exposure dose irradiated on the wafer by using plural blades 2100 attached to plural combination links 2200. The blade 2100 is connected to the combination link 2200 via a blade pivot pin 2300, and the combination link 2200 is connected to a push rod 2500 via a link pivot 2400. The exposure area shaping means 2000 determines a shape of the exposure area by pushing and pulling the push rod 2500 and by moving each blade 2100 to an arbitrary position via the combination link 2200. Here, FIG. 8 is a view for explaining a structure of the conventional exposure area shaping means 2000.
In view of the energy efficiency, the chromatic aberration and the environmental sensitivity, a recently developed slit-scan exposure apparatus includes a catadioptric optical system as a projection optical system that includes plural mirrors and lenses, and defines the exposure area as an arc opening shape. Therefore, the exposure area shaping means needs to correct the uneven exposure by locally changing the opening width of the arc exposure area. However, when the above conventional exposure area shaping means is applied to the exposure area that has an arc-shaped opening, pushing and pulling of the inner correcting position, for example, would result in changes of the outer correcting position.
FIG. 9 is a plane view showing an end surface shape of an arc-shaped metal plate having a pushing/pulling mechanism in the conventional exposure area shaping means. Since FIG. 9 is of bilateral symmetry, the left side is omitted. L0 is an end surface shape at the standard state. P00 is a center position at which the pushing/pulling mechanism is attached. P01 is an inner correcting position at which the pushing/pulling mechanism is attached. P02 is an outer correcting position at which the pushing/pulling mechanism is attached. The outer correcting position P02 is arranged around the exposure area.
For example, when the inner correcting position P01 is pushed and pulled from the standard state L0 in order to correct the uneven exposure, the expansion and contraction of the minute deformations of the arc-shaped metal plate is negligible. Therefore, the correcting position P01 rotates around the center position P00, and turns to a corrected position P11. On the other hand, the outer correcting position P02 turns to a corrected position P12 so that a distance between the inner and outer corrected positions P11 and P12 is equal to a distance between the correcting positions P01 and P02. More specifically, the outer correcting position P02 rotates around the link pivot pin, and turns to the corrected position P12 that offsets from the correcting position P02 in the X direction, since the movement of the minute deformation in the Y direction is negligible. Thus, the end shape L0 at the standard state deforms, and turns to the end surface shape L1 after the deformation.
When the inner correcting position P01 is pushed and pulled, the state becomes as if the corrected position P02 is pushed and pressed, as apparent from FIG. 9, although the outer correcting position P02 is not pushed or pulled. When the inner correcting position P01 is pushed and pulled in order to correct the uneven exposure up to the desired accuracy, the uneven exposure at the correcting position P02 or around the exposure area deteriorates, since the outer correcting position P02 is located around the exposure area. It is conceivable that the outer correcting position P02 is pushed and pulled so as to correct the uneven exposure around the exposure area, but the throughput deteriorates and the uneven exposure is not always corrected to the desired accuracy.
While it is known that the opening width of the exposure area preferably forms an approximate quadratic curve, the conventional exposure area shaping means shapes the opening by bending the arc-shaped metal plate and the opening shape of the exposure area becomes a cubic curve from the beam deformation theory. Even when the arc-shaped metal plate is pushed and pulled so that the uneven exposure becomes minimum at the inner and outer correcting positions P01 and P02, the uneven exposure at an intermediate position between the inner and outer correcting positions P01 and P02 cannot be corrected completely. FIG. 10 is a graph showing a relationship between the slit direction and the corrected amount, when the uneven exposure is corrected to 6%.
Referring to FIG. 10, the ideal curve ya is a quadratic curve expressed by Equation 1 below:ya=Ax2  [EQUATION 1]
The actual corrected curve yb is a cubic curve from the beam deformation theory, and expressed by Equation 2 below, where E is a modulus of longitudinal elasticity, i is a second moment, L is an outer correcting position, and L1 is an inner correcting position:yb=P2/6Ei×(2L3−3L2×(L−x)+(L−x)3)−P1/6Ei×(2L13−3L12×(L1−x)+(L1−x)3)  [EQUATION 2]                where 0<x<L1; andyb=−P2/6Ei×(2L3−3L2×(L−x)+(L−x)3)+P1L13/3Ei×P1×L12×(L1−x)/2Ei        
where L1<x<L
FIG. 10 is a graph of weighting coefficients P1 and P2 so that the corrected curve yb accords with an ideal curve ya at the inner and outer correcting positions P01 and P02. It is understood from FIG. 10 that yb do not accord with ya between the inner and outer correcting positions P01 and P02, and the uncorrectable residue occurs. FIG. 11 is a graph showing a corrective residue amount, i.e., yb−ya, calculated from the graph shown in FIG. 10, and it is understood that the corrective residue amount of 0.19% occurs. This corrective residue amount is not negligible from the tolerance of the uneven exposure required for the recent highly integrated semiconductor devices.